[ovirt-devel] virtio-scsi

Marcus White roastedseaweed.k at gmail.com
Sat Jun 7 02:15:39 UTC 2014

I had some basic questions, was asking them on the kvm list but it
probably makes more sense here:)

The questions are about virtio-scsi. I would appreciate any help.

1. Is virtio-scsi via QEMU a zero copy operation from guest to disk?
The vhost-LIO as I understand it is zero copy, wasnt sure about QEMU.
With the VM and the QEMU thread part of the same process, it would be
good to know the flow and where the copies occur, if they do.

2. When the block layer underneath QEMU(assuming the QEMU does talk to
the block device and not sg, for example), if an error code comes in,
is it converted to a SCSI response before being passed to the guest?

3. Are there any other performance tweaks that would help in both the
QEMU case and the LIO case?

Thanks in advance:)

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